Remote indicating system



Nov. 27, 1945.

C. W. SHERWIN REMOTE INDICATING SYSTEM Filed Jan. 18, 1944 WNW U-UUUUUV DETQ'C TED OUTPUT IN VEN TOR.

CHA L MERS W SHERW/A/ fTf/arrft;

ROTARY TRANSFORMER OUTPUT INPU T TO R0 TARY TRANSFORMER AND GRIDS 0F DETECTORS Patented Nov. 27, 1945 REMOTE INDICATING SYSTEM Chalmers W. Sherwin, Belmont, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of War Application January 18, 1944, Serial No. 518,777

4 Claims.

The invention described herein may be manufactored and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to a remote indicating 4 system and particularly to give position indications at one or more remote stations of apparatus going through cyclic movements.

It is old in the art to have what is in effect a rotary transformer at both sending and receiving stations for transmitting position indications. The rotary transformer at the sending station is coupled to the apparatus whose position is to be transmitted to one or more remote stations. Alternating currents excite both the transmitting and receiving transformers and cause the receiving transformer to assume a position corresponding to the position of the transmitting transformer. Such systems known as Selsyns have been in use for a long time.

These system are generally used where a remote accurate manual control of apparatus is necessary. There are many instances, however, where a remote indication only of the position of an apparatus is desired and in such instances the complexity, weight and expense of a Selsyn system becomes objectionable.

Thus as an example, it may be desired to rotate a directional antenna array and transmit the instantaneous antenna position to a remote station. Other fields of utility are giving remote indications of a compass, clocks and many other devices.

In general, this invention provides a remote indicating system wherein only one rotary trans- 1 former is used. This transformer is at the transmitting station and may have one winding thereof energized by alternating current of substantially uniform amplitude and frequency, which current may be designated as a carrier current. For practical purposes, such a carrier current may have a frequency in the audible range, such as 5,000 cycles per second, so that iron core transformers may be used efficiently. The secondary of this transformer is adapted to be rotated or turned with the device whose position is to be indicated. The output of this secondary transformer is thereupon fed through a suitable pushpull detecting circuit the output of which yields a low frequency current whose magnitude and polarity are a simple function of the position of the secondary.

For a further description of the invention, reference will now be made to the drawing wherein Figure 1 shows a circuit diagram of the remote indicating system and Figure 2 shows the wave forms in various portions of the system.

A rotary transformer l0 may be disposed at a transmitting station. Rotary transformer H1 may be of any type whatsoever and is here shown as having an iron core. Transformer ID ha a primary ll energized from a suitable source of unmodulated alternating current which may for example have a frequency of 5,000 cycles per second. Transformer in has a secondary l2 which may be mechanically mounted so that the coupling with the primary may be varied. Secondary I2 may be tied mechanically or in any other fashion to a mechanical device whose rotary position is to be indicated at some remote point.

The output of secondary I2 is fed from terminals l 3 and I4 to a suitable transmission line l5 and IE to a receiving station. Transmission line l5 and I6 feed secondary energy directly to grids 28 and 2| of a pair of vacuum tube amplifiers 22 and 23. Vacuum tubes 22 and 23 have cathodes 24 and 25 connected to a ground 26. Grid resistors 28 and 29 are connected respectively from grids 20 and 2| to ground. Anode 30 and 3| are connected to primary winding 33 of a push-pull transformer 34, primary 33 having a center tap 35 between which center tap and ground 26 a source of B potential 36 is disposed. It is clear that .vacuum tubes 22 and 23 are in push-pull relation.

Transformer 34 has its secondary 38 provided with a grounded center tap 39 and outer terminals 40 and 4| respectively. Terminal 40 is connected to anode 42 of a vacuum tube 43. Grid 44 of thi tube is connected through a grid resistor 45 to junction point 46, the latter being in an output lead 41 connected to cathode 48. Terminal 40 is also connected by wire to cathode 51 of a vacuum tube 52 having its anode 53 con nected to junction point 45. Grid 55 is connector through a grid resistor 56 to cathode 51. A transformer secondary 58 is connected from cathode 51 through a blocking condenser 59 to grid 55. Another transformer secondary 60 is similarly connected from cathode 48 through a blocking condenser 6 I to grid 44.

Terminal 4| of the transformer i connected to cathode of a vacuum tube 65 whose anode 61 is connected to an output lead 68. Vacuum tube 56 has its grid 69 connected through a grid resistor 10 back to cathode 65. Cathode 55 is also connected to anode 12 of a vacuum tube 13 whose cathode 14 is connected directly to anode 61 of vacuum tube 65. Vacuum tube 13 has its grid 15 connected through a grid resistor 15 back to cathode 14. [A transformer secondary 11 is connected from cathode 85 of vacuum tube 68 through a blocking condenser 18 to grid 69 of that tube.

Likewise transformer secondary 80 is connected between cathode 14 of vacuum tube 13 through a blocking condenser 8| to grid 15 of that tube. Transformer secondaries 58, 60, 11, and 80 are all energized from a primary winding 83 also at the receiving station and connected in parallel to primary ll of rotary transformer l0. Secondary windings 58, 60, I1, and 80 are identical and so poled as to impress at any instant the same polarity on the grids of the four vacuum tubes to which they are connected.

Across the output leads 4! and 68 there may be connected two condensers 85 and 86 in series with their common junction 81 grounded. The output may be fed into a zero center meter or any other indicating means.

The operation of this system is as follows. Assume that alternating current of 5,000 cycles per second is impressed on primaries l I and 83 of the two transformers. Due to the action of primary winding 83, there will be impressed upon the grids of vacuum tubes 43, 52, 66, and I3 alternating potentials of 5.000 cycles per second of substantially equal amplitude and all in phase. At the same time, alternating current in primary winding l I will induce suitable potentials in secondary winding l2. The polarity and amplitude of these potentials will be a direct function of the rotary position 12 with respect to II.

Let it be assumed that a positive peak of the 5,000 cycle current is being impressed upon primary windings H and 83. Let it also be assumed that the position of secondary I2 is such that a positive potential appears at terminal I3 and a negative potential appears at terminal l4. This will result in vacuum tube 22 conducting while vacuum tube 23 will be cut off. Hence space current will flow in the upper portion of primary winding 33 of push-pull transformer 34. This will induce a voltage in secondary winding 38 and this voltage for ease of analysis will be assumed to be positive at terminal 40 and negative at terminal 4|. The positive voltage at terminal 40 will result in some space current passing through vacuum tube 43, the amount of space current and the portion of the conducting one-half positive cycle depending upon the bias of grid 44. At this particular instant, however, grid 44, asis true of the remaining grids in this series of tubes, is positive so that vacuum tube 43 becomes con-. ducting. The negative potential at terminal 4| with the positive bias of grid 69 will result in space current flowing through vacuum tube 66. By suitable adjustment of the biasing potentials induced in transformer secondaries 58, 60, I1, and 80, it is possible to have the conducting vacuum tube operate only at the positive peak of the bias cycle on each grid. Thus a short pulse will pass through vacuum tubes 43 and 66 to charge series condensers 85 and 86. Condensers 85 and 86 should be small enough so that during each conducting period of the detector tubes, the condensers become substantially full charged.

On the part of the carrier cycle below the positive peak, there will be no conduction in any detector tube since the grids of such tubes will be at or below cutoff. On a reverse or negative part of the modulating cycle, due to reversed polarity of rotary transformer secondary I2, vacuum tubes 52 and 13 will conduct but only at the instant when the grid bias is at the positive peak. This will result in an output 01. pulses of negative polarity.

It is evident that output leads 4! and 68 will thus have potentials whose values are constantly changing with reference to ground both in an absolute and algebraic sense. The potentials from leads 41 and 68 may then be amplified or applied to any suitable indicating means such as 9. voltmeter, for example, with a scale suitably calibrated for the indications to be giyen.

As shown in Figure 2, the actual output of the system consists of a. series of small steps at varying potentials. Each step begins on the time axis at the instant that the detector tubes become conductive and this may be determined by the ordinate of the unmodulated alternating potentials impressed upon the detector tube grids. As preiviously indicated, the detector tubes are operated 'in such a manner that the tubes are below cutoff for most of the grid potential cycle except for a short time at which the grid bias is substantially at its maximum positive value. This may be accomplished in various manners such as by a direct biasing potential superimposed upon the alternating potentials or by adjusting the values of the resistors and capacitance in the grid circuit so that the time constant of the grid circuit has the proper value for accomplishing the above.

Thus if the grid bias frequency is 5,000 cycles per second, then each period is 200 microseconds. If the time constant of the grid circuit, i. e. product of grid resistance and blocking condenser with grid to cathode tube resistance assumed infinite, is large compared to 200 microseconds, then the grid potential variations will remain small during most of the cycle. At the positive peak of grid bias the grid rises above cutoff and the grid to cathode resistance is small, compared to the grid resistor, so that the time constant of the grid circuit is now comparatively small. When a detector tube conducts, the blocking condenser in the grid circuit of such tube will become rapidly charged within a, few microsceconds. This will of course occur only during the existence of the positive potential peak on the grid. At the end of the short charging period of the blocking condenser, the full difference in potential induced in the secondary winding supplying the grid with bias potential will now be impressed across the blocking condenser. .The grid side of the blocking condenser will be negative when' the charging is complete, it being understood of course that this terminal of the condenser drops in potential during the charging process. The difference in potential across the blocking condenser should be suflicient to bias the grid to cutoff. When the tube is thus cut off, the grid resistor completes the condenser circuit. As the potential impressed upon the condenser from the secondary winding drops, the blocking condenser discharges with the grid still remaining below cutoff. The reversal of potential on the blocking condenser will have no effect on the grid cutoff potential due to the long time constant of the condenser circuit. Thus by making the time constant about three or more periods, i. e. something of the order of 600 microseconds or longer, the blocking condenser cannot become charged sufficiently to raise the grid above cutofl.

By choosing a sumciently high frequency for system will tend to average the output so that a close approximation to the original input to the indicating system may be obtained.

What is claimed is:

1. An indicating system comprising a transformer having windings relatively movable to vary the coupling from a maximum through zero to another maximum, said winding movement being mechanically connected to an apparatus whose position is to be indicated, means for impressin an unmodulated alternating current on the primary, connections from said secondary to a push-pull detecting system, said system having two rectiflers in each leg thereof, said two rectifiers being in parallel with the cathode of one connected to the anode of the other, means for rendering all rectiflers conductive simultaneously only during the peak value in one algebraic sense only of each cycle of said unmodulated alternating current and means for utilizing said detected output togive indications of the condition of said transformer.

2. The system of claim 1 wherein said connections include a stage of push-pull amplification controlled from said transformer secondary.

3. The system of claim 1 wherein said rectiners are three element vacuum tubes and wherein the means for rendering said rectiflers conductive consists of means for applying said unmodulated alternating current on the grids of said vacuum tubes with the tubes operating in such a manner that said tubes are at cutofl except during the positive peaks of the potentials impressed on said grids.

4. The system of claim 1 wherein said rectifiers consist of three element vacuum tubes, 

